Four-wheel drive is a type of drive system in which both front wheels are connected to their own differential and axles, and both rear wheels are connected to their own differential and axles. Between these two differentials, a transfer case is provided so as to transfer driving force.
Four-wheel drive enables a vehicle to travel off-road or on a declined road, and makes it easier to drive in snow such that the safety of the vehicle is improved.
However, because conventional four-wheel drive systems are provided with a transfer case, efficiency of transferring driving force is lower than with two-wheel drive, and the gross weight of the vehicle substantially increases.